why are thyroid hormones exceptions to the usual mode of non

why are thyroid hormones exceptions to the usual mode of nonsteroid hormone functioning

Solution

The hormones are two types-steroid hormones and non steroid hormones. The steroid hormones are derived from cholesterol and the non steroid hormones are like amines, peptides, polypeptides and proteins or glycoproteins that are derived from amino acids. The hormones bind to the receptor on the target cells and trigger the changes even when they are in extremely low concentrations.

The non steroid hormones like amines, peptides or proteins bind to the receptors on the target cell membranes. When the hormones bind to the receptors the receptors activity site interacts with the membrane proteins. The hormone triggering the series of biochemical events is called first messenger. The biochemical molecules in the cell induce specific changes in target cell in response to the hormone binding with the receptor and these are known as second messengers. For example, cAMP is the second messenger. The entire chemical communication pathway is known as signal transduction.

Thyroid hormone is a nonsteroid hormone and is a amino acid derivative. Thyroid hormones are small iodinated amino acids that apparently enter their target cells and bind to receptors already associated with a DNA molecule within the nucleus of the target cell. Therefore, unlike other nonsteroid hormones, thyroid hormones functions in the mode of nuclear-receptor mechanism.